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Previous research has presented contradictory evidence on the ability of overall dynamic body acceleration (ODBA) to predict mass-corrected oxygen consumption (sVO2) in airbreathing diving vertebrates. We investigated a potential source of these discrepancies by partitioning the ODBA-sVO2 relationship over 3 phases of the dive cycle (transiting to and from depth, bottom time, and post-dive surface interval). Trained Steller sea lions Eumetopias jubatus executed 4 types of dives to 40 m (single dives, long-duration dive bouts of 4-6 dives, short-duration dive bouts of 10 or 12 dives, and transit dives with minimal bottom duration). Partitioning single dives by dive phase showed differing patterns in the ODBA-sVO2 relationship among dive phases, but no significant linear relationships were observed. The proportion of the dive cycle spent tran siting to and from the surface was a significant predictive factor in the ODBA-sVO2 relationship, while bottom duration or post-dive surface interval had no effect. ODBA only predicted sVO2 for dives when the proportion of time spent transiting was small. The apparent inability of ODBA to reliably predict sVO2 reflects differences in the inherent relationships between ODBA and sVO2 during different phases of the dive. These results support the growing body of evidence that ODBA on its own is not a reliable field predictor of energy expenditure at the level of the single dive or dive bout in air-breathing diving vertebrates likely because ODBA (a physical measure) cannot account for physiological changes in sVO2 that occur during the different phases of a dive cycle.

We tested the ability of overall dynamic body acceleration (ODBA) to predict the rate of oxygen consumption ( $$s\dot{V}_{{{\text{O}}_{2} }}$$ ) in freely diving Steller sea lions (Eumetopias jubatus) while resting at the surface and diving. The trained sea lions executed three dive types—single dives, bouts of multiple long dives with 4–6 dives per bout, or bouts of multiple short dives with 10–12 dives per bout—to depths of 40 m, resulting in a range of activity and oxygen consumption levels. Average metabolic rate (AMR) over the dive cycle or dive bout calculated was calculated from $$s\dot{V}_{{{\text{O}}_{2} }}$$ . We found that ODBA could statistically predict AMR when data from all dive types were combined, but that dive type was a significant model factor. However, there were no significant linear relationships between AMR and ODBA when data for each dive type were analyzed separately. The potential relationships between AMR and ODBA were not improved by including dive duration, food consumed, proportion of dive cycle spent submerged, or number of dives per bout. It is not clear whether the lack of predictive power within dive type was due to low statistical power, or whether it reflected a true absence of a relationship between ODBA and AMR. The average percent error for predicting AMR from ODBA was 7–11 %, and standard error of the estimated AMR was 5–32 %. Overall, the extensive range of dive behaviors and physiological conditions we tested indicated that ODBA was not suitable for estimating AMR in the field due to considerable error and the inconclusive effects of dive type.

International audience; This study investigated prey captures in free-ranging adult female Australian fur seals (Arctocephalus pusillus doriferus) using head-mounted 3-axis accelerometers and animal-borne video cameras. Acceleration data was used to identify individual attempted prey captures (APC), and video data were used to independently verify APC and prey types. Results demonstrated that head-mounted accelerometers could detect individual APC but were unable to distinguish among prey types (fish, cephalopod, stingray) or between successful captures and unsuccessful capture attempts. Mean detection rate (true positive rate) on individual animals in the testing subset ranged from 67-100%, and mean detection on the testing subset averaged across 4 animals ranged from 82-97%. Mean False positive (FP) rate ranged from 15-67% individually in the testing subset, and 26-59% averaged across 4 animals. Surge and sway had significantly greater detection rates, but also conversely greater FP rates compared to heave. Video data also indicated that some head movements recorded by the accelerometers were unrelated to APC and that a peak in acceleration variance did not always equate to an individual prey item. The results of the present study indicate that head-mounted accelerometers provide a complementary tool for investigating foraging behaviour in pinnipeds, but that detection and FP correction factors need to be applied for reliable field application.

Imposed 48-hr periods of fasting in six young (6 to 24 months) female northern fur seals did not decrease metabolism or increase thermoregulatory costs, but were more detrimental in the summer than the winter when higher metabolic costs normally required to fuel seasonal growth led to higher rates of mass loss., An unexpected shortage of food may affect wildlife in a different way depending on the time of year when it occurs. We imposed 48 h fasts on six female northern fur seals (Callorhinus ursinus; ages 6–24 months) to identify times of year when they might be particularly sensitive to interruptions in food supply. We monitored changes in their resting metabolic rates and their metabolic response to thermal challenges, and also examined potential bioenergetic causes for seasonal differences in body mass loss. The pre-fast metabolism of the fur seals while in ambient air or submerged in water at 4°C was higher during summer (June to Sepember) than winter (November to March), and submergence did not significantly increase metabolism, indicating a lack of additional thermoregulatory costs. There was no evidence of metabolic depression following the fasting periods, nor did metabolism increase during the post-fast thermal challenge, suggesting that mass loss did not negatively impact thermoregulatory capacity. However, the fur seals lost mass at greater rates while fasting during the summer months, when metabolism is normally high to facilitate faster growth rates (which would ordinarily have been supported by higher food intake levels). Our findings suggest that summer is a more critical time of year than winter for young northern fur seals to obtain adequate nutrition.